Thanks Phil for the advice. On Sysconfig I have added I-Mail-Spam-Revdns and I have also put the Match and Set values as advised, but still it does no work.

I think the point you are missing is the one Andy Lubel raised: Andy Lubel wrote:

...

And you have a SMTP gateway tagging this? Something like SpamAssasin or the likes?

What he is saying is that your incoming email must be being processed and tagged in the headers FIRST before OTRS can use the tags to filter out spam. OTRS is not a spam filter itself, it can only filter based on the message headers. My previous message was an example of the headers that MY ISP puts on my email headers. Your ISP might not have a spam system, or may have a different one. If they have a different one, you will have to ask them what they use and what headers to expect. If they do not have a spam system, you will have to implement one yourself, as described in the OTRS manual. I hope this helps you to understand and crack your spam problem!